FIGS. 1A and 1B show views for explaining an example of the branch portion of a conventional multi-core optical fiber tape. FIG. 1A illustrates the configuration of a multi-branch tube used to form the branch portion and FIG. 1B illustrates the configuration of the branch portion.
A multi-branch tube 31 is constituted by a optical fiber fixing portion 32 which receives and fixes a multi-core optical fiber tape 1, a plurality of single-core optical fiber protection tubes 33 which are disposed on the side opposite to the optical fiber fixing portion 32 so that branched single-core optical fibers 2 are passed therethrough respectively, and a branch portion accommodation space 34 which is formed between the optical fiber fixing portion 32 and the single-core optical fiber protection tubes 33, those portions 32, 33 and 34 being formed integrally with each other.
As shown in FIG. 1B, the multi-core optical fiber tape 1 is fixed at the vicinity of an end portion thereof in the optical fiber fixing portion 32 of the multi-branch tube 31, and the single-core optical fibers 2 branched from the optical fiber tape 1 are inserted through and protected by the single-core optical fiber protection tubes 33 of the multi-branch tube 31. Thus, the branch portion is formed.
FIGS. 2A and 2B show views for explaining another example of the branch portion of a conventional multi-core optical fiber tape. FIG. 2A illustrates the configuration of a multi-branch tube used to form the branch portion and FIG. 2B illustrates the configuration of the branch portion.
This example is different from the example of FIG. 1A in that a multi-branch tube 31 has no portion for fixing a multi-core optical fiber tape 1 and a protection tube 35 for protecting the multi-core optical fiber tape 1 is integrally formed. Accordingly, the optical fiber tape 1 inserted into the protection tube 35 is not fixed thereat.
The foregoing conventional branch portion of the multi-core optical fiber tape 1 is a result of contrivance as to a manner how to make the multi-core optical fiber tape 1 branch into plurality of the single-core optical fibers 2 not to be too extreme, and the branch portion is designed in consideration of the arrangement of the single-core optical fiber protection tubes 33 so that no force is exerted on the single-core optical fibers 2 in the respective single-core optical fiber protection tubes 33. The branch portion is however ineffective in protection of the branching out single-core optical fibers 2 in the branch portion accommodation space 34 between the end portion of the optical fiber tape 1 and the single-core optical fiber protection tubes 33.
There is therefore a problem in that when resin or the like is poured into the branch portion accommodation space 34 so as to fix the single-core optical fibers 2, force is exerted on the single-core optical fibers 2 to thereby cause increase of optical loss. Further, in the case there no resin is poured into the space 34, the increase of optical loss is similarly caused because of lack of stability of the optical fibers 2 in the branch portion accommodation space 34.